The present invention relates to a process for producing a ferrite single crystal for high frequency.
Generally, Ni-Zn ferrite has magnetic properties superior to those of Mn-Zn ferrite in a high frequency region, for example, above 10 MH.sub.Z. The reason is that the Ni-Zn ferrite has a higher crystal magnetic anisotropy constant and specific resistance.
In growing Ni-Zn ferrite single crystal by Bridgman's method under atmospheric pressure, a different phase is formed if Fe.sub.2 O.sub.3 content is less than 55 molar %, whereby a mixed crystal thereof with a spinel phase is formed. This fact has been confirmed by X-ray analysis, etc. Therefore, for obtaining the pure spinel phase, Fe.sub.2 O.sub.3 content must be more than 55 molar %. However, when Fe.sub.2 O.sub.3 content is more than 50 molar %, magnetite (FeO.Fe.sub.2 O.sub.3) is formed, specific resistance is reduced due to the presence of Fe.sup.2+ and high frequency magnetic properties are degraded due to eddy current loss to make the same useless in a high frequency region.
Accordingly, for growing Ni-Zn single crystal, Fe.sub.2 O.sub.3 content should be adjusted to around 50 molar % and the presence of Fe.sup.2+ should be avoided. Consequently, the growing must be effected under a high oxygen partial pressure (at least 100 Kg/cm.sup.2) in the prior art. This is unsuitable for mass production, though it is allowable in production on an experimental scale.